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排序方式: 共有523条查询结果,搜索用时 187 毫秒
91.
Winfried Nischkauer Marie-Alexandra Neouze Frank Vanhaecke Andreas Limbeck 《Mikrochimica acta》2015,182(15-16):2369-2376
92.
J. Málek R. A. Evarestov A. N. Ermoshkin B. Hejda K. Polák 《Czechoslovak Journal of Physics》1975,25(11):1201-1207
One-electron energy levels of NiF
6
4–
cluster, effective charges qNi and qF, parameters 10Dq,
crys
,,f
s
,f
andf
were calculated using four alternative models of population analysis. The influence of the size of basis set was also investigated. Based on comparison of results it was shown that all evaluated quantities are dependent on the manner of division of overlap charge made up by virtual 4s and 4p nickel orbitals. To remove this discrepancy it was suggested to assign the whole 4s and 4p population to ligands. In this case all calculated parameters are nearly independent of a model of population analysis and the size of basis set and their values correspond better to experimental data. 相似文献
93.
Balcaen LI De Schamphelaere KA Janssen CR Moens L Vanhaecke F 《Analytical and bioanalytical chemistry》2008,390(2):555-569
In order to study the effect of anthropogenic substances on freshwater and marine ecosystems and to develop methods to derive
water-quality criteria, ecotoxicological testing is required. While toxicity assessments are traditionally based on dissolved
metal concentrations, assuming that toxicity is caused by waterborne metal only, it was recently pointed out that also the
dietary exposure route should be carefully considered and interpreted in regulatory assessments of zinc. In this context,
the aim of this experimental study was to develop a method which allows the uptake of waterborne and dietary zinc by Daphnia magna and the interaction between both exposure routes to be studied. Therefore, the setup of a dual isotopic tracer study was
required. During several days, daphnids were exposed to 67Zn and 68Zn via the dietary and the waterborne routes, respectively, and after several time intervals the daphnids were sampled and
subjected to isotopic analysis by means of inductively coupled plasma mass spectrometry (ICP–MS). In order to obtain reliable
and accurate results for zinc, special care was taken to prevent contamination and to deal with the spectral interferences
traditionally hindering the determination of zinc. The figures of merit of both a quadrupole-based ICP–MS instrument equipped
with a dynamic reaction cell, and a sector field ICP–MS unit were studied, and it was concluded that by using a sector field
mass spectrometer operated at medium mass resolution all interferences could be overcome adequately. Although the set-up of
the exposure experiments seems to be rather simple at first sight, it was shown in this work that several (dynamic) variables
can have an influence on the results obtained and on the subsequent data interpretation. The importance of these confounding
factors was examined, and on the basis of preliminary calculations it became clear that not only the isotopic composition
of the daphnids has to be studied—adequate monitoring of the isotopic composition of the dissolved phase and the algae during
the exposure of the daphnids is also required to accurately discriminate between uptake from water and from food.
Lieve I.L. Balcaen and Karel A.C. De Schamphelaere contributed equally to this study 相似文献
94.
Pol VG Calderon-Moreno JM Thiyagarajan P 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13640-13645
A single-step solvent-, catalyst-, and template-free synthesis process to prepare photoluminescent pencils of ZnO either in micro- or in nanosize diameters from a single precursor is demonstrated. The thermolysis of Zn's acetate dihydrate (ZAD) precursor in a closed stainless steel reactor at 700 degrees C under autogenic pressure (6.5 MPa), yielded carbon sphere-decorated ZnO micropencils (ZnO-M's). The ZnO-M's have novel room-temperature photoluminescence (PL) with well-defined emission peaks at the green, yellow, orange, and red regions of the visible spectra while suppressing the blue region. On the contrary, the thermolysis of ZAD in a closed stainless steel reactor at 700 degrees C with released pressure yielded uniformly carbon-coated ZnO nanopencils (ZN's). The coated carbon in ZN's quenches the complete UV-vis PL; however, after annealing ZN's at 600 degrees C/2 h in air, the UV PL is dominant, and the visible PL is suppressed. The carbon coating (partly or completely) on the one-dimensional (1D) ZnO surfaces plays an important role to modify PL properties. The insight into the reaction mechanism was gained through in situ mass spectrometry measurements. The as-prepared ZnO-M's and ZN's have been systematically characterized to determine their morphology, structure, and composition. 相似文献
95.
Wolpher H Sinha S Pan J Johansson A Lundqvist MJ Persson P Lomoth R Bergquist J Sun L Sundström V Akermark B Polívka T 《Inorganic chemistry》2007,46(3):638-651
A series of bis(terpyridine)RuII complexes have been prepared, where one of the terpyridines is functionalized in the 4'-position by a phosphonic or carboxylic acid group for attachment to TiO2. The other is functionalized, also in the 4'-position, by a potential electron donor. In complexes 1a, 3a, and 4a,b, this donor is tyrosine or hydrogen-bonded tyrosine, while in 2a it is carotenoic amide. The synthesis and photophysical properties of the complexes are discussed. On irradiation with visible light, the formation of a long-lived charge-separated state was anticipated, via primary electron ejection into the TiO2, followed by secondary electron transfer from the donor to the photogenerated RuIII. However, such a charge-separated state could be observed with certainty only with complex 2a. To explain the result, quantum chemical calculations were performed on the different types of complexes. 相似文献
96.
Pol VG Langzam Y Zaban A 《Langmuir : the ACS journal of surfaces and colloids》2007,23(22):11211-11216
A simple microwave irradiation method for the large-scale synthesis of submicrometer-sized TiO2 rods at normal atmospheric pressure and the boiling temperature of the solvent is demonstrated. It is emphasized that only 1-3 min of microwave irradiation is adequate to react tetra-isopropyl orthotitanate with ethylene glycol to produce rods of titanium glycolate [TG] with diameters of approximately 0.4 microm and lengths up to 5 microm. The as-formed TG rods, followed by calcination under air for 2 h, fabricated anatase (500 degrees C) and rutile (900 degrees C) titania without changing their rod-shaped morphology. The crystallinity, structure, morphology, and thermal analysis are carried out by several techniques. A mechanism based on microwave superheating phenomena is presented with the support of previous reports and several control experiments. 相似文献
97.
V. D. Kagan N. A. Red’ko N. A. Rodionov V. I. Pol’shin 《Physics of the Solid State》2000,42(8):1414-1421
A peak is detected on the dependence of the diffusion-induced thermopower on transverse magnetic field in degenerate semiconducting alloys n-Bi1?x Sbx (0.07≤x≤0.15) doped with tellurium donor impurity. The temperature gradient is directed along the bisector axis C 1 of the monocrystalline sample and the magnetic field is along the triad axis C 3. The electron spectrum of the Bi-Sb alloys under investigation consists of three equivalent ellipsoids with distinctly different effective masses along the axes of the ellipsoid (m ∥/m ⊥). A simple kinetic theory shows that the presence of the peak on the diffusion thermopower is a manifestation of this strong anisotropy in the electron spectrum and of the additive contribution of all three ellipsoids to electron transport. The nonmonotonic dependence of thermopower on the transverse magnetic field makes it possible to determine the electron relaxation time, while the temperature dependence of this relaxation time can be used to separate the relaxation time for electrons scattered from ionized impurities and from acoustic phonons. 相似文献
98.
A Borel derivative on the hyperspace 2
X
of a compactumX is a Borel monotone mapD: 2
X
→2
X
. The derivative determines a Cantor-Bendixson type rank δ:2X → ω1 ∪ {∞} . We show that ifA⊂2
X
is analytic andZ⊂A intersects stationary many layers δ−1({ξ}), then for almost all σ,F∩δ−1({ξ}) cannot be separated fromZ ∩∪
a<ξ
δ−1({a}) (and also fromZ ∩∪
a>ξ
δ−1({a}) by anyF
σ-set. Another main result involves a natural partial order on 2
X
related to the derivative. The results are obtained in a general framework of “resolvable ranks” introduced in the paper.
During our work on this paper the second author was a Visiting Professor at the Miami University, Ohio. This author would
like to express his gratitude to the Department of Mathematics and Statistics for the hospitality. 相似文献
99.
Jianping Lu Antisar R. Hlil Allan S. Hay Tony Maindron Jean‐Pol Dodelet Jennifer Lam Marie D'Iorio 《Journal of polymer science. Part A, Polymer chemistry》2000,38(15):2740-2748
The design and synthesis of novel charge (hole‐ or electron‐) transport materials have been the focus of much research in recent years because of their wide variety of applications. In this study, three high molecular weight poly(arylene ether)s, 6a–c, containing naphthyl‐substituted benzidine moieties have been synthesized from carbamates derived from bisphenols. After masking with n‐propyl isocyanate, the carbamate is stable, can be readily purified by recrystallization from toluene, and can be polymerized directly with difluoro compounds under mild conditions. The resulting polymers possess high glass‐transition temperatures, excellent thermal stability, and good film‐forming properties. In comparison, the poly(arylene ether)s 6a′–c′, synthesized from unprotected bisphenol, have lower molecular weights and wider polydispersity and contain some brown impurities. Preliminary experiments show that both 6a and 6a′ can function well as hole‐transport materials in light‐emitting diodes. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2740–2748, 2000 相似文献
100.
The following question is considered: Which quasi-Sasakian (cosymplectic, Sasakian, or proper quasi-Sasakian) structures admit nontrivial concircular transformations of their metrics (i.e., determine Fialkow spaces), and under what conditions. It is proved that any cosymplectic manifold is a Fialkow space. Necessary and sufficient conditions for a Sasakian or a quasi-Sasakian manifold to be a Fialkow space are obtained. A fairly large class of Sasakian manifolds which are not Fialkow spaces is described. 相似文献